Method of constructing building structures of zig-zag profile

ABSTRACT

A method of constructing building structures having walls of zig-zag profile, the steps of arranging panels in a juxtaposed, hinged-together, coplanar relationship, lifting the entire assembly at predetermined lifting points to erect the structure and to simultaneously form the zig-zag configuration by virtue of the gravity-caused angular movement of the panels with respect to one another and grouting all the hinges to &#39;&#39;&#39;&#39;freeze&#39;&#39;&#39;&#39; the erected structure.

United States Patent 1191 Salas 1 1 Dec. 17 1974 [54] METHOD OFCONSTRUCTING BUILDING 3,461,626 8/1969 Aitken 52/71 STRUCTURES OF ZlGZAG PROFILE 3,494,092 2/1970 Johnson et a1 52/745 3,593,482 7/1971Johnson 52/745 [76] Inventor: Frank D- Salas, 05 Pa sal A 3,600,8706/1971 Greenbalgh 52/745 N tle NJ. 07110 D u y FOREIGN PATENTS ORAPPLICATIONS [22] 1971 653,204 11/1962 Canada 52/86 [211 App] 39 229,8903/1925 Great Britain 52/432 Primary Examiner-Frank L. Abbott [52] US. Cl52/742, 52/18,5522//77415, Assistant Examiner Leslie A Brown 51 Im. c1.E04g 21/14 Agent firm-Gab Keleme" [58] Field of Search 52/745, 18, 742,743, 64,

52/70, 71, 747, 285, 583, 432 ABSTRACT A method of constructing buildingstructures having References Cited walls of zig'zag profile, the stepsof arranging panels in UNITED STATES PATENTS a juxtaposed,hinged-together, coplanar relationship, 1,361,831 12/1920 Crew 52/69lifting the entire assembly at predeterfnined lifting 1,393,699 10 1921Purcell et a1 52 583 P011118 to erect the Structure and toslmultaneously 3,057,119 10/1962 Kessler 52/86 form the zig-zagconfiguration by virtue of the gravity- 3,300,942 1/1967 Horstman 52/742caused angular movement of the panels with respect 3,331,181 7/1967Schmidt 52/745 to one another and grouting all the hinges to freeze3,374,588 3/1968 Alfrey et a1 52/747 the erected structure. 3,407,54610/1968 Yates et al 52/64 3,443,344 5/1969 Williams 52/64 3 Claims, 14Drawing Figures PAIEMEQ EW 3.854.266

- sum 10F 5 INVENTOR FRANK 0. .534 AA 5 ATTO R N EY SHEET 2 0F 5 PATENTEL EU 71974 INVENTO'R ATTORNEY PAIENTE LEE 1 71974 SHEET 3 0F 5 aNvE NTORFHA/V A 0. SAZAS ATTORNEY PATENTEL SE81 7 i974 SHEET u (If 5 INVENTORFRANK 0. 5144/25 ATTORNEY METHOD OF CONSTRUCTING BUILDING STRUCTURES OFZIG-ZAG PROFILE BACKGROUND OF THE INVENTION This invention relates to amethod of constructing building structures of the type that have aplurality of walls each, formed of generally elongated panels attachedto one another at adjoining edges and forming an angle so as to producea zigzag profile. Structures of this zig-zag type have a particularlyhigh rigidity and therefore a high load-carrying capacity.

According to one known method,;the entire interconnected structure isshipped to the construction site in an accordionlike collapsed state, inwhich the hingedly interconnected panels are stacked face-toface so thatthe angle between adjoining panels is close to zero. An end view of suchcollapsed or folded structure shows substantially the same configurationas in its final position. At the site of erection, the accordionlikefolded structure is positioned upright and pulled open by a force normalto its span. This method of erection is practiced mostly withlight-weight, thin, flexible materials wherein the panels have beenpreformed by suitable folding. These lightweight structures usually formthe building itself which is generally of temporary nature (tents,temporary light shelters, and the like). This method is not adaptable topanels of heavyweight and rigid material such as concrete, since theweight and bulkiness of the interconnected components render itimpractical for shipment and unfolding to a final position at the siteof erection.

In another conventional method, the building structure of zig-zagprofile, particularly if it is of the heavyweight type, is assembled,panel by panel, with the aid of construction scaffolds. According tothis method, each panel is mounted in its final position and thus norelative angular movement of the panels takes place.

Known methods of assembling structures of zig-zag wall profile,particularly of the type that consist of heavyweight panels, such asconcrete slabs, is a relatively lengthy, slow and circumstantialprocess, normally requiring extensive scaffolding and costly form work.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention toprovide an improved method for the construction of buildings orstructures having multiple walls of zig-zag profile. This method permitsa greatly simplified erection of the components and assemblies involvedand a wide choice of building configurations and construction materials.

Briefly stated, according to the invention, trapezoidal and/ortriangular panel elements are first juxtaposed and hingedlyinterconnected at the construction site to form a planar, coherentassembly, wherein the panels form as many series as there are walls inthe eventual structure.

As a subsequent step, hoisting means are attached to the panel assemblyat predetermined lifting points.

Subsequently, the assembly is lifted whereupon, by virtue of thecooperation between the gravitational force and the lifting forceattacking at particularly lectcd lifting points, the walls of thestructure and the zig-zag profile of each wall are gradually formed.During the lifting operation the roof walls are raised to apredetermined height while the terminal walls swing inwardly towards oneanother until the desired, predetermined angle with respect to theground is obtained.

Thereafter, by means of grouting or the like, all the hinges between allthe panels forming the structure are frozen and the terminal walls areanchored to the ground, or a supporting structure, whereupon a rigid,permanent, high load resistant building structure is obtained.

The invention will be better understood, as well as further objects ofthe invention will become more apparent, from the ensuing detailedspecification taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic perspective viewof an exemplary building structure in an erected position;

FIG. 2 is a schematic perspective view of the same building structurelaid out coplanar prior to erection;

FIGS. 3-5 illustrate schematically and in perspective views successivesteps of erecting a building structure according to the invention;

FIGS. 6-9 are schematic perspective views of four further exemplarybuilding structures in an erected position;

FIG. 10 is a fragmentary perspective view of a form for casting abuilding structure which can be constructed with the method according tothe invention;

FIG. 11 is a fragmentary perspective view of an assembly of hinged slabsobtained from casting in a form shown in FIG. 10 and FIGS. 12, 13 and 14are schematic perspective views of a building structure in successiveoperational phases of the method according to the invention.

GENERAL DESCRIPTION OF THE METHOD Turning first to FIG. 1, there isshown a particular configuration of a typical structure in its final,permanent position subsequent to the completion of the constructionmethod practiced according to the invention. As seen, this structurecomprises three walls 1, 2 and 3. Walls 1 and 3 are terminal walls, thefree ends of which are supported on or in the ground. The wall 2 will behereinafter designated as the roof wall. The distance between the twoterminal walls 1 and 3 measured at the ground is the span S, while thehorizontal dimension normal to the span is the length L of thestructure. The vertical distance between the roof wall and the ground isthe height H.

Each wall has a zig-zag profile with alternating ridges and valleys. Itis noted that in this particular configuration any imaginary verticalplane normal to the length dimension L and containing a ridge (as viewedfrom the outside) of the roof wall 2, also contains a valley in each ofthe terminal walls 1 and 3. Stated in different terms, each ridge 4 inthe roof wall 2 changes into a valley 5 in terminal wall 1 and into avalley 6 in terminal wall 3.

Each wall of the building structure consists of a series of trapezoidalpanels. The latter are designated at 7a, 7b and 70, forming walls 1, 2and 3, respectively.

Turning now to FIG. 2, as an initial step of the method according to theinvention. all the panels are juxtaposed and hinged together at theconstruction site.

The panels which are all trapezoids in this example, are arranged in aplurality of adjacent series. Each panel series will eventuallyconstitute one wall of the structure. The panels belonging to the sameseries are juxtaposed in such a manner that identical long sides ofadjoining panels are immediately adjacent and are in exact alignmentwith one another.

The panels of one series (e.g., panels 7a) are so arranged and hinged tothe panels of an adjacent series (panels 7 b) that the immediatelyadjacent short sides of two adjoining panels 7a and 7b are in exactalignment with one another.

It will be apparent from a comparison of FIGS. 1 and 2 that the widthand number of panels in one series, as well as the angle betweenadjoining panels, will determine the eventual length L of the structure.

Each panel is hingedly joined to the immediately adjacent panel at leastat two points on each side.

As a subsequent step, the location of lifting points on the presentlyplanar panel assembly is determined. The primary consideration indetermining the lifting points is to ensure that the initial, overallplanar assembly will be transformed into a structure where all the wallsare of a zig-zag profile. In the given example the central panel seriesconsisting of panels 7b will form the roof wall 2 and consequently, thisentire wall will be spaced from the ground. As a comparison of FIGS. 1and 2 indicates, the shorter one of the two long, parallel sides of eachtrapezoid will form a ridge 4. The straight line continuation of eachsuch designated ridge is the longer one of the two long, parallel sidesof adjoining panels 7a and 7c of the terminal walls 1 and 3. They willform valleys 5 and 6, respectively. It will now be apparent that inorder to obtain a zig-zag profile of the roof structure, lifting points.have to be located on each ridge of the roof. The number of liftingpoints on any ridge of the roof wall is not critical for practicing theinvention; for the purpose of reducing erection stresses, however, theoptimal solution would be to have as many lifting points along oneparticular ridge as practical. As a practical solution, it has beenfound satisfactory to have two lifting points per ridge; each liftingpoint being close to the ends adjoining the panels that form theterminal wall.

Subsequently, cables of a hoisting device, such as a crane, are attachedto the lifting points, as illustrated in FIG. 3. The choice of theparticular hoisting device is not critical and may be guided solely bypractical considerations. Thus, for example, instead of a crane, it isfeasible to use a trolley-type hoist or helicopters.

FIGS. 4 and 5 illustrate the building structure in an intermediate andin a final position, respectively, during and upon completion of thelifting operation.

As the structure is being lifted by cables at the previously determinedlifting points, the formation of the accordion-type configuration of notonly the roof wall 2, but also of the terminal walls 1, 3 willsimultaneously and progressively take place. During this operation, twotypes of angular changes will take place simultaneously by virtue of thehinged attachment between panels and the interaction between the liftingand the gravitational forces: in the first place, the originally 180angle between adjacent panels in each series will decrease leading tothe zig-zag profile of each wall and, in the second place, theoriginally 180 angle between adjacent panel series will decrease wherebythe angular disposition of one wall with respect to an immediatelyadjacent wall will appear. The decrease in the first angle shortens thelength of the assembly to approach the predetermined length L and thedecrease of the second angle reduces the span of the structure toapproach the predetermined span S. During these angular changes, thedistance of the roof wall 2 from the ground gradually increases untilthe structure approaches its predetermined height H. It is thus seenthat the building structure of predetermined design is formed from theentirely planar panel assembly by imparting thereto a dual folding,during the course of which there are simultaneously (a) formed thestructurally rigid zig-zag profile of each wall and (b) effected theangular disposition of one wall with respect to an adjoining other wall.As mentioned before, all the angles are initially and decrease graduallyas the dual folding progresses. During this dual folding operation noneof the panels need to undergo a deformation and therefore the panels maybe, and preferably are, of practically entirely rigid material, such asconcrete. Thus, at any given moment during the dual folding operationand after the completion thereof, between any two adjoining panels inany wall, the angle will have a constant value along the joining line oftwo such panels.

When the predetermined dimensions (span, length and height) of thestructure are obtained, the lifting operation is terminated andthereafter steps are taken to prevent any further angular change in therelative position of the panels with respect to one another. This isachieved by rigidizing the hinges between panels, for example, by meansof grouting, and anchoring the lower ends of the terminal walls to theground or to a supporting structure.

The aforedescribed method is adapted to be used with a great variety ofstructural configurations consisting of walls having a zig-zag profile.Thus, in addition to the two terminal walls which engage the ground or asupporting structure, the building structure may have two or more roofwallsinstead of the single roof wall 2 of the structure shown in FIG. 1.Thus, the structure shown in FIG. 6 is similar to that of FIG. 1, exceptthat the roof is formed of two roof walls 2a and 2b.

In general, if the building structure includes more than one roof wall,the lifting speed for different points of the roof wall panels isdifferent. It is the highest at those points of a ridge that will beeventually positioned highest in the erected structure and decreases forthose ridge points that are closer to the terminal walls.

The invention may also be practiced in case of a structure having onlyterminal walls (A-frame) as shown in FIG. 7.

The method according to the invention and described hereinbefore inconnection with structures formed solely of trapezoidal panels may beequally practiced in case of structures which include triangular panels.Two such examples are illustrated in FIGS. 8 and 9.

In FIG. 8, the roof wall formed of trapezoidal panels is connected tothe terminal walls, also formed of trapezoidal panels, not directly asshown, for example, in FIG. 1, but with the interposition of triangularsubpanels 8.

The structure depicted in FIG. 9 is developed from the configurationaccording to FIG. 8 by reducing the length of the adjoining panel sidesof the roof to zero.

In this manner the roof wall is formed only of triangular panels 9meeting in points 10 situated along the length dimension of thestructure.

Turning now to the determination of lifting points in case of thestructures according to FIGS. 8 and 9, it is apparent that at least one(but preferably more) lifting point should be selected on each ridge 11in FIG. 8. Further, on the same structure, there should be one liftingpoint at the intersection between each valley 12 of the roof wall andeach valley 13 of the terminal walls.

In the structure according to FIG. 9, there should be a lifting point ateach peak 10 and also, at the intersection between each valley 14 of theroof wall and each valley 15 of the terminal walls.

Generalizing the selection of lifting points with regard to thestructures illustrated in FIGS. 1, 6, 8 and 9, it may be said that thereshould be at least one lifting point between any two valleys lying in avertical plane that is substantially normal to the length dimension ofthe structure. If such two valleys are interconnected by a ridge (suchas ridge 4 in FIG. I or ridge 11 in FIG. 8), then preferably severallifting points are used, distributed along such ridge. If, on the otherhand, two valleys intersect (such as shown in FIG. 9 at points 10 and16), then the point of intersection will be designated as a liftingpoint.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION In thedescription that follows, there will be set forth an on-the-site castingand erection of a reinforced concrete building structure integrallyincorporating the aforedescribed method.

As a first step, in the ground where the structure is to be erected, twoparallel linear trenches are exca vated. They are spaced from oneanother at a distance that corresponds to the predetermined span of thebuilding structure, while their lengths correspond to the predeterminedlength of the building. The depth and the width of each trench are sodesigned as to receive, for anchoring and support purposes, thelowermost portion of a terminal wall of the building structure.

As a next step, over and symmetrically with respect to the two trenchesa planar mold or form is built having a plurality of partitions formingspaces of trapezoidal and/or triangular configuration. These spaces aredisposed with respect to one another in the same relationship as theintended building structure when laid out prior to the liftingoperation. Further, between each trapezoidal and/or triangular space,the partitions define clearances, the purpose of which will become clearhereinafter.

As shown in fragmentary FIG. 10, the partitions 17 are spaced from oneanother to define continuous clearances 18 therebetween. In eachpartition there are inserted eye bars 19 each having an eye 20 arrangedin the aforenoted clearances 18 and the opening of which lies in avertical plane. In each individual clearance 18 the eyes 20 of all theeye bars 19 are arranged in axial alignment. For reinforcing purposes acontinuous mesh 21 made for example of wire extends horizontally overthe entire form and thus also passas through the partitions and throughthe clearances 18.

In a further step, concrete, or any other suitable casting material (forexample, gypsum) is poured in the form between clearances so as to formtrapezoidal and- /or triangular panels connected by the mesh. Subsequentto the hardening of the casting material, the partitions are removed.Each planar trapezoidal or triangular slab now has embedded in each ofits sides eye bars 19 with axially aligned eyes 20.

Turning now to FIG. 11, through each series of eyes 20 in one linearclearance 18, there are inserted rigid metal rods or cables 22, thelength of each equals approximately the length of the two immediatelyadjacent panel sides. Thus, the eye bars 19 embedded in the cast slaband the rods 22 threaded therethrough form a hinge connection betweenany two adjacent trapezoid or triangular slabs. It is to be noted thathe adjacent slabs are also connected by the mesh 21.

Thereafter, the lifting operation may be performed as described earlierin the specification. It is also noted that the lifting cables may befastened to the appropriate rods 22 or to the eye bars 19 which coincidewith the predetermined lifting points on each panel. The mesh 21 willbend in the clearances 18 by virtue of the weight of the cast slabs,thus permitting the latter to assume the aforedescribed angularrelationship with respect to one another.

As soon as the free ends of the terminal walls drop into the preformedtrenches, the lifting operation is terminated.

In order to render the structure entirely rigid, the clearances betweenthe panels are grouted and further, concrete is poured into the trenchesto provide an anchor for the terminal walls.

FIG. 12 illustrates the relationship between two parallel lineartrenches 23 and a panel assembly having walls 1, 2 and 3 prior to thelifting operation.

FIG. 13 depicts the building structure after the side walls 1 and 3 havedropped into the respective trenches 23 and the lifting mechanism hasbeen removed.

FIG. 14 shows the trenches 23 filled with an anchoring material, such asconcrete, to permanently fix the building structure in its erectedposition.

The aforedescribed construction method greatly simplifies the castingand erection of concrete building structures. It is seen that notransporting of the concrete slabs is necessary since the entirestructure is erected directly from the position in which it was cast.

What is claimed is:

1. A method of constructing a building structure of predetermined designformed of walls each having a zig-zag profile bounded by alternatingridges and valleys, each wall consisting of a plurality of edge-wiseadjoining and interconnected planar, straight-edged polygonal panelsdisposed at an angle to one another, comprising the following steps:

A. excavating two parallel trenches spaced from one another at adistance corresponding to the intended width of the building structure,each trench having a length corresponding to the intended length of thebuilding structure, each trench having a width and a depth adapted toreceive lowermost zones of two walls of the building structure;

B. juxtapositioning and hingedly interconnecting all panels to form acoplanar, coherent assembly, panels constituting one and the same wallfollow each other along the length dimension of said structure and aredisposed at an angle of with respect to one another, panels constitutingdifferent walls follow each other along the span dimension of saidstructure, wherein adjoining walls are disposed at an angle of 180 withrespect to one another, said coplanar, coherent assembly being laid oversaid trenches;

C. imparting a dual folding to said coplanar assembly in a singleoperation for gradually forming said zigzag profile of all of said wallsand, simultaneously, gradually decreasing the angle between adjoiningwalls, wherein all the angles of inclination between any two adjoiningpanels in any wall decrease in unison and have all identical magnitudesat any moment of the folding operation, whereby each panel maintainsunchanged its planar configuration at all times; I

D. dropping, in the course of said dual folding operation, saidlowermost zones of two walls into said trenches, whereby saidpredetermined design is reached;

E. discontinuing, subsequent to step (D), said dual folding operation;

F. fixing, subsequent to step (E), all the hinges between all the panelsto obtain a permanently rigid building structure of said predetermineddesign; and

G. filling, subsequent to step (E), said trenches with .a material topermanently immobilize said lowermost zones.

2. A method of constructing a building structure of predetermined designformed of walls made of casting material, each wall having a zig-zagprofile and consisting of a plurality of edgewise adjoining andinterconnected planar, straight-edged polygonal cast slabs disposed atangle to one another, comprising the following steps:

A. excavating two parallel trenches spaced from one another at adistance corresponding to the intended span of the completed buildingstructure, each trench having a width and depth adapted to receive foranchoring and support, the lowermost wall portion of the buildingstructure;

B. building, over said trenches, a planar form having partitionsenclosing upwardly open spaces of the shape of the slabs to be formed,said spaces adjoining one another with a clearance on each side;

C. placing eyebars in each partition for each side of each space, theeyes of said eye bars being arranged in a vertical plane and in ahorizontal alignment in each clearance;

D. pouring a casting material in each partition, subsequent to steps (B)and (C), to obtain a coplanar cast slab assembly wherein slabsconstituting one and the same wall follow each other along the lengthdimension of said structure and are disposed at an angle of with respectto one another, slabs constituting different walls follow each otheralong the span dimension of said structure wherein adjoining walls aredisposed at an angle of 180 with respect to one another;

E. placing rod means in each clearance to pass through each eye disposedtherein; said eye bars and rod means forming hinges;

F. removing said form after hardening of the casting material subsequentto step (D);

G. attaching hoisting means to a plurality of predetermined liftingpoints on said coplanar slab assembly;

H. imparting a dual folding to said coplanar slab aswhereby each panelmaintains unchanged its planar configuration at all times;

. dropping, in the course of said lifting operation,

said lowermost wall portions into said trenches, whereby saidpredetermined height is reached; and

J. fixing, subsequent to step (H), all the hinges between all the castslabs to obtain a permanently rigid building structure.

3. A method as defined in claim 2, including the step of pouringconcrete into said trenches subsequent to the termination of step (I).

1. A method of constructing a building structure of predetermined designformed of walls each having a zig-zag profile bounded by alternatingridges and valleys, each wall consisting of a plurality of edge-wiseadjoining and interconnected planar, straight-edged polygonal panelsdisposed at an angle to one another, comprising the following steps: A.excavating two parallel trenches spaced from one another at a distancecorresponding to the intended width of the building structure, eachtrench having a length corresponding to the intended length of thebuilding structure, each trench having a width and a depth adapted toreceive lowermost zones of two walls of the building structure; B.juxtapositioning and hingedly interconnecting all panels to form acoplanar, coherent assembly, panels constituting one and the same wallfollow each other along the length dimension of said structure and aredisposed at an angle of 180* with respect to one another, panelsconstituting different walls follow each other along the span dimensionof said structure, wherein adjoining walls are disposed at an angle of180* with respect to one another, said coplanar, coherent assembly beinglaid over said trenches; C. imparting a dual folding to said coplanarassembly in a single operation for gradually forming said zig-zagprofile of all of said walls and, simultaneously, gradually decreasingthe angle between adjoining walls, wherein all the angles of inclinationbetween any two adjoining panels in any wall decrease in unison and haveall identical magnitudes at any moment of the folding operation, wherebyeach panel maintains unchanged its planar configuration at all times; D.dropping, in the course of said dual folding operation, said lowermostzones of two walls into said trenches, whereby said predetermined designis reached; E. discontinuing, subsequent to step (D), said dual foldingoperation; F. fixing, subsequent to step (E), all the hinges between allthe panels to obtain a permanently rigid building structure of saidpredetermined design; and G. filling, subsequent to step (E), saidtrenches with a material to permanently immobilize said lowermost zones.2. A method of constructing a building structure of predetermined designformed of walls made of casting material, each wall having a zig-zagprofile and consisting of a plurality of edgewise adjoining andinterconnected planar, straight-edged polygonal cast slabs disposed atangle to one another, comprising the following steps: A. excavating twoparallel trenches spaced from one another at a distance corresponding tothe intended span of the completed building structure, each trenchhaving a width and depth adapted to receive for anchoring and support,the lowermost wall portion of the building structure; B. building, oversaid trenches, a planar form having partitions enclosing upwardly openspaces of the shape of the slabs to be formed, said spaces adjoining oneanother with a clearance on each side; C. placing eyebars in eachpartition for each side of each space, the eyes of said eye bars beingarranged in a vertical plane and in a horizontal alignment in eachclearance; D. pouring a casting material in each partition, subsequentto steps (B) and (C), to obtain a coplanar cast slab assembly whereinslabs constituting one and the same wall follow each other along thelength dimension of said structure and are disposed at an angle of 180*with respect to one another, slabs conStituting different walls followeach other along the span dimension of said structure wherein adjoiningwalls are disposed at an angle of 180* with respect to one another; E.placing rod means in each clearance to pass through each eye disposedtherein; said eye bars and rod means forming hinges; F. removing saidform after hardening of the casting material subsequent to step (D); G.attaching hoisting means to a plurality of predetermined lifting pointson said coplanar slab assembly; H. imparting a dual folding to saidcoplanar slab assembly in a single operation for gradually forming saidzig-zag profile of all of said walls and, simultaneously, graduallydecreasing the angle between adjoining walls by lifting, subsequent tostep (G), said cast assembly by said hoisting means to a predeterminedheight, whereby all the angles of inclination between any two adjoiningslabs in any wall decrease in unison and have all indentical magnitudesat any moment of the folding operation, whereby each panel maintainsunchanged its planar configuration at all times; I. dropping, in thecourse of said lifting operation, said lowermost wall portions into saidtrenches, whereby said predetermined height is reached; and J. fixing,subsequent to step (H), all the hinges between all the cast slabs toobtain a permanently rigid building structure.
 3. A method as defined inclaim 2, including the step of pouring concrete into said trenchessubsequent to the termination of step (I).